Inkjet printing is often used to reproduce continuous-tone, e.g., photographic, images using a limited number of ink colors. Inkjet printers commonly use a CMYK color model, e.g., in which the ink colors are cyan, magenta, yellow, and black. Ink colors can be 1) blended or 2) spatially averaged (or both) to provide colors not represented by the individual inks. For example, human perception will spatially average a pattern of red and yellow pixels to yield a perception (optical illusion) of orange. The yellow dots can be achieved using yellow ink, while the red dots can be achieved by blending or overlaying magenta and yellow inks.
“Continuous-tone” images may be converted to a printable, e.g., “half-tone”, image form suitable for inkjet printing progressively. The difference between the color in the continuous-tone image and its “approximation” color in the target image is called a “quantization residual” or “error”. “Error diffusion” is a technique in which the quantization residuals of previously processed pixels are distributed to neighboring pixels so that the target image will closely match the continuous tone image. Thus, for example, error diffusion can make it more likely that some neighbors of a red pixel are yellow where the objective is to provide a perception of orange.